Internal shoe-drum brakes

ABSTRACT

In an internal shoe-drum brake in which an actuator for separating the shoes is located between the shoes at one end, the other ends of the shoes abut on members slidable in a stationary body and separated by an intermediate component which includes a stop limiting movement of one member towards the other and may include means for automatically adjusting the separation of the members.

United States Patent 1191 Farr 1 Oct. 1, 1974 [54] INTERNAL SHOE-DRUM BRAKES 3,532,193 10 1970 Kaiser 188/795 P Inventor: y Phillip Reginald Farr, 3,744,595 7/l973 Adams l88/l96 DX Kenilworth, England [73] Assignee: Girling Limited, Birmingham, Primary Examine"Dl-lane Reger E l d Attorney, Agent, or FirmScrivener, Parker,

S & Cl k 22 Filed: Feb. 22, 1973 cmener ar e [2]] Appl. No.: 334,612

[57] ABSTRACT [30] Foreign Application Priority Data Marv 3, 1972 Great Britain 9920/72 I n int rnal hoe-drum brake in which an actuator Mar. 9, l972 Great Britain 10952/72 for eparating the shoes is located between the shoes at one end, the other ends of the shoes abut on mem- [52] [1.3. Cl 188/795 P, 188/196 D berg slidable in a stationary body and separated by an [51] Int. Cl. F16d 65/56 i t rm di te om onent which includes a stop limit- Field of Search 188/795 GC, ing movement of one member towards the other and 196 D may include means for automatically adjusting the separation of the members. [56] References Cited UNlTED STATES PATENTS 9 Claims, 6 Drawing Figures 3,200,909 8/1965 Swift 188/795 GT PATENTEB GET 1 74 SHEET 2 OF 4 INTERNAL SHOE-DRUM BRAKES According to our invention, in an internal shoe-drum brake an actuator for separating the shoes is located between the shoes at one end, and between the other ends of the shoes there is located an abutment unit comprising a body fixed to the stationary back plate of the brake, a first normally non-rotatable member slidable in the body for co-operation with the end of one shoe, a second normally non-rotatable member slidable in the body for co-operation with the end of the other shoe and an intermediate component extending between the' members and including a stop or stops adapted to engage with a part of the body to limit movement of one member towards the other.

In a convenient arrangement the first and second members comprise pistons or plungers axially slidable in aligned bores in the body, and the intermediate component comprises a spindle which is in screw-threaded engagement with one or both members and is preferably rotatable by automatic adjusting means to adjust the effective length of the assembly formed by the two members and the spindle.

One of the members is preferably arranged to be axially slidable relative to the spindle and may be actuated by fluid pressure to produce a two-leading-shoe operation of the brake, usually in the normal forward direction of rotation of the brake drum, the brake conveniently being arranged to produce duo-servo action in the opposite direction of rotation of the drum.

In another arrangement both members may be actuated by fluid pressure which ensures that in duo-servo operation of the brake in said opposite direction of rotation of the drum the secondary shoe is always positively actuated even if fading of the primary shoe lining reduces the input force to the assembly to an unacceptable value.

In an alternative arrangement the intermediate component comprises a two-part spindle of which one part is in screw-threaded engagement with one member and the other part is in direct or indirect screw-threaded engagement with the other member, the two parts being alternatively rotatable by automatic adjusting means to adjust independently the position of each member in the body to compensate for wear of the co-operating shoe.

It will be appreciated that the side loads from the shoes are taken by the members which are axially slidable in the body and the spindle is not subjected to side loads and can readily be rotated by automatic adjusting means.

Some practical embodiments of our invention are illustrated by way of example in the accompanying drawings in which:

FIG. 1 is a front elevation of a brake,

FIG. 2 is a vertical section on the line 22 of FIG.

FIG. 3 is a horizontal section on the line 3--3 of FIG.

FIG. 4 is a section similar to FIG. 3 of a modified form of abutment unit,

FIG. 5 is another section similar to FIG. 3 of another modified form of abutment unit,

FIG. 6 is another section similar to FIG. 3 showing a still further form of abutment unit.

In the brake shown in FIGS. 1, 2 and 3 two opposed arcuate brake shoes 1, 2 are mounted on a stationary back plate 3 and carry friction linings 4 for engagement with a rotatable brake drum (not shown).

The shoes are separated at their upper ends to apply the brake by a wedge 5 actuated by a fluid-pressure motor indicated at 6.

Between the lower ends of the shoes is located an abutment unit 7 incorporating means for separating the shoes and for adjusting them automatically to compensate for wear of the linings.

The abutment unit, as shown in section in FIG. 3, is an open-ended fluid pressure cylinder 8 mounted on the back plate 3. Pistons 9, 10 work in opposite ends of the cylinder. The piston 9 has an axial recess in its outer end in which is rotatably mounted a spigot 11 on the inner end of a tappet 12 adapted to engage the shoe 1. A tappet 13 for engagement with the shoe 2 is integral with the piston 10. The pistons are provided with the usual seals 14. A spindle 15 extends axially within the cylinder through an annular shoulder or partition 16. One end of the spindle is in screw-threaded engagement with a blind axial bore in the inner end of the piston 9 and the other end is in screw-threaded engagement with a nut 17 which can slide axially but is keyed against rotation in a counterbored part of a blind axial bore in the inner end of the piston 10. The sxrewthreads on opposite ends of the spindle are right and left handed respectively so that rotation of the spindle moves the pistons axially in opposite direction.

The inner end of the piston 10 is normally spaced a short distance from the adjacent end of the shoulder 16, the gap being indicated at 18.

The spindle has a collar 19 of substantial diameter adapted to bear on the opposite end of the shoulder 16.

An intermediate portion of the spindle is formed with a screw-thread 20 of steep pitch, and working on this portion is an internally threaded drive ring 21 of which the outer surface is coned for co-operation with an interal frusto-conical face 22 on the shoulder 16. The ring is urged into clutching engagement with the face 22 by a coiled spring 23, and a concentric spring 24 is arranged between the collar 19 and an internal annular step 25 in the shoulder 16.

To apply the brake, fluid under pressure is supplied to the motor 6 to separate the upper ends of the shoes and to the inner ends of the pistons 9, 10.

Assuming that normal forward rotation of the brake drum is anti-clockwise as indicated by the arrow in FIG. 1 the shoe 1 will be urged into engagement with the drum by the wedge actuator and the servo effect due to the contact of the shoe with the drum will force the tappet 12 and piston 9 inwardly in the cylinder 8 against the fluid pressure applied to the inner end of the piston. The force applied to the piston 9 will be transmitted to the spindle 15 but as the collar 19 on the spindle is in engagement with the shoulder 16 in the cylinder no force will be transmitted to the piston 10. That piston will be urged outwardly by the fluid pressure acting on its inner end and will urge the lower end of the shoe 2 outwardly into engagement: with the brake drum so that both shoes act as leading shoes.

When the brake drum is rotating in the reverse direction, the shoe 2 applies a servo action to the piston 10 and it can move inwardly owing to the clearance 18 between it and the shoulder 16. When this clearance is exceeded owing to'wear of the shoe-linings movement of the piston 10 to the left (in FIG. 3) takes up the play in the threaded connection between the nut 17 and the spindle l5 and in addition moves the spindle 15 to the left to reduce the clutching engagement between the drive ring 21 and the face 22 so that it can rotate as the spindle moves to the left through it.

The desired minimum shoe clearance in the off position of the brake is allowed for by play in the various screw-threaded connections. When this clearance is exceeded owing to wear of the shoe-linings movement of the piston to the left (in FIG. 3) takes up the clearances and moves the drive ring 21 to the left to reduce the clutching engagement with the face 22 so that it can rotate as the spindle moves to the left through it.

The spring 23 overcomes the friction in the thread 20 on the spindle which would otherwise tend to carry the drive ring to the left with the spindle. The spring 24 prevents the spindle from being rotated as the ring rotates due to torque generated by the friction in the thread.

When the brake is released the shoes are returned by the usual return springs and the parts of the abutment do not move and no adjustment takes place, but the adjuster is prepared to adjust on the next brake application with the drum rotating in the normal forward direction.

On the next occasion the brake is applied with the drum revolving in the forward direction the spindle moves to the right. The initial movement of the spindle 15 forces the drive ring 21 into firm engagement with the face 22 to prevent rotation of the drive ring so that as the spindle 15 moves further to the right it is forced to rotate by the fixed drive ring thereby moving the pistons apart to adjust the shoes, until the spindle is prevented from further movement by the collar 19 abutting shoulder 16.

The ratio of the pitch of the thread on the spindle to those of the threaded engagements of the spindle with the pistons is such that only a small part say one thirtieth of the wear is taken up on each adjustment so that the adjuster is of the incremental type.

In the modification shown in FIG. 4 no means are provided for applying pressure fluid to the pistons which need not be provided with seals but the arrangement is othewise the same and the same reference numerals have been applied to corresponding parts.

The nut 17 can be fixed in the piston 10 which does not need to slide independently of the spindle.

With this form of abutment the brake acts as a leading-trailing shoe brake in the forward direction and as a duo-servo brake in the reverse direction.

In both of the embodiments described above teeth 26 are formed on the outer end of the piston 9 to allow it to be rotated manually with a suitable tool to contract the adjuster and to enable the brake drum to be removed in the event of grooving of the drum, for example, or to release a jammed adjuster. Rotation of the piston without affecting the shoe 1 is permitted by the rotatable spigot connection between the piston and the tappet 12.

An important advantage of our improved brake shoe abutment is that it automatically compensates for differential shoe-lining wear in the case where the lining of the primary shoe 1 wears more than that of the secondary shoe 2. It will be appreciated that the adjuster senses wear of the primary shoe 1 only, i.e., the distance the spindle travels from the collar abutment position to the shoe fully applied position. If the shoe 1 wears more than the shoe 2 the consequent adjustment will be excessive for the shoe 2. This means that the shoe 2 will contact the brake drum first and the reaction from this will cause the collar 19 to move away from the shoulder 16, thereby causing the brake to act temporarily as a duoservo brake in the forward direction. This will apply the shoe 2 with extra force causing more rapid wear until engagement of the collar 19 with the shoulder 16 is re-established and the position corrected.

If on the other hand there is excessive wear of the shoe 2 this will not be sensed by the adjuster which only senses wear of the shoe 1, and movement of the shoe 2 would then become excessive.

To ensure that this situation never occurs various measures may be used.

One is to reduce the input to the shoe 2 relative to the shoe 1, either by applying a higher actuating force to the upper ends of the shoes than to their lower ends or by using a stronger return spring at the bottom than at the top.

Other possible measures are to use a coarser thread on the right hand end of the spindle 15 so as always to adjust the shoe 2 more than the shoe 1; to fit a harder lining to the shoe 2; or to have a shorter arc of lining on the shoe 1 than on the shoe 2.

These measures should ensure that the shoe 1 always requires more adjustment than the shoe 2 to bring the self-compensating feature of the adjuster into effect.

With the modified form of abutment shown in FIG. 5 the brake will act as a two-leading shoe brake in both directions of rotation of the drum.

In this arrangement there are two pistons 30, 31 working in opposite ends of a cylinder 32 and carrying at their outer ends tappets 33, 34 in rotatable spigot engagement with the pistons. The piston is in screwthreaded engagement with one end of an axially extending spindle 35 having a collar 36 adapted to abut against an internal shoulder 37 in the cylinder.

The other end of the spindle is of hexagonal or other non-circular cross-section and is in sliding engagement with a bore in a sleeve 38 of which the outer surface is in screw-threaded engagement with a blind axial bore in the piston 31. A drive ring 39 is in screw-threaded engagement with a thread 40 of steep pitch on the spindle and the peripheral surface of the ring is coned for engagement with a frusto-conical face 41 on the shoulder 37 towards which it is urged by a spring 42.

Teeth 43 are formed on the outer ends of both pistons for adjusting them manually and independently by means of a suitable tool.

In the modified form of abutment unit shown in FIG. 6 the body 50, which is adapted to be secured to the back plate of the brake, is formed with aligned bores 51, 52 in which pistons 53 and 54 respectively work. The pistons carry at their outer ends tappets 55 and 56 for engagement with the ends of the brake shoes.

A stud 57 having a head 58 at its inner end is in irreversible screw-threaded engagement with a blind bore 59 in the piston 53, and a similar stud 60 having a head 61 at its inner end is in irreversible screw-threaded engagement with a blind bore 62 in the piston 54.

An axial extension 63 of the stud 57 is a sliding fit in a blind bore 64 in the stud 60, and a spring 65 located between the extension and the end of the bore maintains an axial load on the screw-threaded engagements between the studs and the pistons.

An internal annular abutment 66 in the body between the bores 51 and 52 has opposed inclined faces 67, 68 co-operating with complementary inclined faces on the heads of the studs, the abutment providing stops for the inward movement of both pistons.

A reversible screw-thread 69 of steep pitch is formed on the extension 63, and a double-coned non-handed drive ring 70 is in engagement with this thread. The ring is urged by a spring 71 into clutching engagement with a coned surface 72 in a recess in the inner end of the stud 60. i

If fluid under pressure is supplied to the actuator 6 and to the abutment unit between the pistons 53 and 54 while the brake drum is rotating in an anti-clockwise direction as seen in FIG. 1 circumferential movement of the shoe 1 is restricted by the engagement of the head of the stud 57 with the face 67 of the abutment 66. The shoe 2 moves through a small angle with the drum and is followed to the right (as seen in FIG. 3) by the piston 54. If excessive wear of the friction surfaces has taken place the clearance between the reversible screw-thread on the extension 63 and the drive ring 70 is taken up and the head of the stud 60 moves away from the face 68 on the abutment. The spring 71 causes the drive ring 70 to follow and the ring rotates to a new angular position on the extension 63.

When the fluid pressure is relieved the shoe return springs return the piston 54, the headed stud 60, and the drive ring 70 towards the face 68 on the abutment, but because the clutch engagement between the drive ring and the stud 60 is now increased the drive ring and the stud rotate together and the stud 60 and the pistons 54 thus take up a new position.

If the drum is rotating clock-wise when the shoes are separated the shoe 2 forces the stud 60 against the face 68 on the abutment. The piston 53 lifts the stud 57 away from the face 67 and if the wear of the shoe 1 is excessive the extension 63 is pulled through the drive ring 70, and the the spring 71 causes the drive ring to rotate around the extension.

When the fluid pressure is relieved the shoe return springs force the drive ring into tight clutching engagement with the stud 60, and as the stud is held against rotation by the friction in the loaded irreversible screwthreaded engagement between the piston 54 and the stud 61, the stud 57 and the extension 63 rotate within the drive ring back to theoff position with the head 58 of the stud against the face 67 on the abutment.

Independent and alternative adjustments are thus provided for the pistons 53 and 54 according to the direction of rotation of the drum.

It will be understood that adjustment only occurs on axial movement of a piston. If the fluid pressureoperated pistons 53 and 54 are replaced by plungers, as in the embodiment shown in FIG. 4, separate means are required for moving the associated shoe ends.

The extension 63 can be rigidly connected to the stud 57 but it has been found sufficient to provide the extension with a head 73 in clutching engagement with the inner end of the stud.

It is an advantage of this construction that the abutment unit incorporates a maximum number of common parts.

If necessary separate means can be used to provide a greater shoe tip effort at the actuated ends of the shoes than at the abutment unit, as for example by using hydraulic pistons of greater diameter in the actuator and/or by using shoe return springs of greater strength.

I claim:

1. An internal shoe-drumbrake in which arcuate shoes are mounted on a stationary back plate and an actuator for separating the shoes is located between the shoes at one end and an abutment unit is located between the other ends of the shoes, said abutment unit comprising a body fixed to the stationary back plate, a flrst normally non-rotatable member slidable in the body for co-operation with one shoe, a second normally non-rotatable member axially slidable in the body for co-operation with the end of the other shoe, and an intermediate component extending between the members and including stops adapted to engage with a part of the body and to limit movement of one member towards the other.

2. An internal shoe-drum brake as in claim 1 wherein said members comprise plungers axially slidable in aligned bores in the body, and the :intermediate component comprises a spindle which is in screw-threaded engagement with at least one of the members and is rotatable by automatic adjusting means.

3. An internal shoe-drum brake as in claim 2 wherein one end of said spindle is in screw-threaded engagement with a blind axial bore in one member and the other end of the spindle is in screw-threaded engagement with a nut slidable but not rotatable in a blind axial bore in the other member, the screw-threads on opposite ends of the spindle being of opposite hands.

4. An internal shoe-drum brake as in claim 2 wherein one end of said spindle is in screw-threaded engagement with one member and the other end is of noncircular cross-section and is slidably engaged in a bore in a sleeve which is in screw-threaded engagement with a blind axial bore in the other member.

5. An internal shoe-drum brake as in claim 2 wherein said automatic adjustment means comprises a drive ring which has a reversible screw-threaded engagement with an intermediate part of the spindle and a springloaded coned clutching engagement with a part of the body, excess axial movement of a member in the application of the brake reducing the clutching engagement of the drive ring with the body and allowing said ring to be rotated by axial movement of the spindle.

6. An internal shoe-drum brake as in claim I wherein said members comprise pistons working in aligned bores in the body, the pistons being provided with seals and means being provided for supplying hydraulic fluid under pressure between the pistons.

7. An internal shoe-drum brake as in claim 1 wherein said stops for the movement of each piston towards the other are formed by opposite ends of an annular internal shoulder in the body.

8. An internal shoe-drum brake as in claim 1 wherein said intermediate component comprises an assembly including a first headed stud in screw-threaded engagement with a blind bore in one member, a second headed stud in screw-threaded engagement with a blind bore in the other member, an axial extension of the first extension of the first headed stud and a drive ring working on said thread and in spring-loaded clutching engagement with the secons stud, the clutching engagement being freed by excess axial movement of the second member in the application of the brake whereby the ring is rotated by axial movement of the extension through it. 

1. An internal shoe-drumbrake in which arcuate shoes are mounted on a stationary back plate and an actuator for separating the shoes is located between the shoes at one end and an abutment unit is located between the other ends of the shoes, said abutment unit comprising a body fixed to the stationary back plate, a first normally non-rotatable member slidable in the body for co-operation with one shoe, a second normally non-rotatable member axially slidable in the body for co-operation with the end of the other shoe, and an intermediate component extending between the members and including stops adapted to engage with a part of the body and to limit movement of one member towards the other.
 2. An internal shoe-drum brake as in claim 1 wherein said members comprise plungers axially slidable in aligned bores in the body, and the intermediate component comprises a spindle which is in screw-threaded engagement with at least one of the members and is rotatable by automatic adjusting means.
 3. An internal shoe-drum brake as in claim 2 wherein one end of said spindle is in screw-threaded engagement with a blind axial bore in one member and the other end of the spindle is in screw-threaded engagement with a nut slidable but not rotatable in a blind axial bore in the other member, the screw-threads on opposite ends of the spindle being of opposite hands.
 4. An internal shoe-drum brake as in claim 2 wherein one end of said spindle is in screw-threaded engagement with one member and the other end is of non-circular cross-section and is slidably engaged in a bore in a sleeve which is in screw-threaded engagement with a blind axial bore in the other member.
 5. An internal shoe-drum brake as in claim 2 wherein said automatic adjustment means comprises a drive ring which has a reversible screw-threaded engagement with an intermediate part of the spindle and a spring-loaded coned clutching engageMent with a part of the body, excess axial movement of a member in the application of the brake reducing the clutching engagement of the drive ring with the body and allowing said ring to be rotated by axial movement of the spindle.
 6. An internal shoe-drum brake as in claim 1 wherein said members comprise pistons working in aligned bores in the body, the pistons being provided with seals and means being provided for supplying hydraulic fluid under pressure between the pistons.
 7. An internal shoe-drum brake as in claim 1 wherein said stops for the movement of each piston towards the other are formed by opposite ends of an annular internal shoulder in the body.
 8. An internal shoe-drum brake as in claim 1 wherein said intermediate component comprises an assembly including a first headed stud in screw-threaded engagement with a blind bore in one member, a second headed stud in screw-threaded engagement with a blind bore in the other member, an axial extension of the first stud in sliding engagement with an axial bore in the second stud, and an internal shoulder in the body for engagement by the inner ends of the studs to limit inward movement of the members.
 9. An internal shoe drum brake as in claim 8 wherein an automatic adjuster is incorporated, the adjuster being formed by a screw-thread of steep pitch on said extension of the first headed stud and a drive ring working on said thread and in spring-loaded clutching engagement with the secons stud, the clutching engagement being freed by excess axial movement of the second member in the application of the brake whereby the ring is rotated by axial movement of the extension through it. 